The present invention relates to a new and improved method for checking or testing the functionality of transmitter-receiver reversing switches present in pulse Doppler-radar installations for protecting the microwave-receiver component, by means of a microwave-checking or testing signal which is supplied to the microwave-receiver component between the antenna and the transmitter-receiver reversing switches.
In radar devices having common transmitter- and receiver antenna there are present reversing switches, usually called TR-tubes or ATR-tubes in duplexer, for rapidly switching the antenna between the transmitter and the receiver. Transmitter-receiving reversing switches must simultaneously protect the receiver from the high HF-energy of the transmitter and along the transmitting path as well as also the receiving path should cause only minimum damping losses, time-delays and distortions.
Particularly great requirements are placed upon the transmitter-receiver reversing switches when the pulse-radar devices operate at relatively small target distance. The corresponding short pulse-travel-times require extremely short, reproducible switching times. It is therefore obvious that a need exists to check the functional reliability of such important elements periodically, at least however prior to placing the radar device into operation.
In German patent publication No. 1,075,685 there is disclosed, for instance, a device for the periodic comprehensive total checking of a radar device. Due to a series of measurements, among others, also the receiver sensitivity, it is thus possible to narrow down errors. A defective transmitter-receiver reversing switch can be equally ascertained with the corresponding expenditure of equipment which is there provided.
Basically, transmitter-receiver reversing switches can be differently constructed (cf. M. Skolnik, Radar Handbook, McGraw-Hill, 1970, Chapter 8.6), but all types, by measurement of the relative throughpass damping, allow for determinations regarding their functional state. In the case of, for instance, transmitter-receiver reversing switches (TR-tubes operating according to the glow discharge principle) it is possible, due to the absorption of gas molecules by the electrodes, that reduced gas pressure prevails internally of the TR-tube or tubes. This brings about correspondingly increased regeneration times (deionization of the tubes after each transmitting pulse, and especially in the case of short distance measurements leads to breakdown of the radar device. Such change of the blocking characteristic brought about by the operating time can be still detected in time by measuring the absolute throughpass damping or by comparative measurements (relative throughpass damping) for different signal flow.